A recent episode of the dystopian television series “Black Mirror” begins with a soldier hunting down and killing hideous humanoids called roaches. It’s a standard science-fiction scenario, man against monster, but there’s a twist: it turns out that the soldier and his cohort have brain implants that make them see the faces and bodies of their targets as monstrous, to hear their pleas for mercy as noxious squeaks. When our hero’s implant fails, he discovers that he isn’t a brave defender of the human race—he’s a murderer of innocent people, part of a campaign to exterminate members of a despised group akin to the Jews of Europe in the nineteen-forties.

The philosopher David Livingstone Smith, commenting on this episode on social media, wondered whether its writer had read his book “Less Than Human: Why We Demean, Enslave, and Exterminate Others” (St. Martin’s). It’s a thoughtful and exhaustive exploration of human cruelty, and the episode perfectly captures its core idea: that acts such as genocide happen when one fails to appreciate the humanity of others.

One focus of Smith’s book is the attitudes of slave owners; the seventeenth-century missionary Morgan Godwyn observed that they believed the Negroes, “though in their Figure they carry some resemblances of Manhood, yet are indeed no Men” but, rather, “Creatures destitute of Souls, to be ranked among Brute Beasts, and treated accordingly.” Then there’s the Holocaust. Like many Jews my age, I was raised with stories of gas chambers, gruesome medical experiments, and mass graves—an evil that was explained as arising from the Nazis’ failure to see their victims as human. In the words of the psychologist Herbert C. Kelman, “The inhibitions against murdering fellow human beings are generally so strong that the victims must be deprived of their human status if systematic killing is to proceed in a smooth and orderly fashion.” The Nazis used bureaucratic euphemisms such as “transfer” and “selection” to sanitize different forms of murder.

As the anthropologist Claude Lévi-Strauss noted, “humankind ceases at the border of the tribe, of the linguistic group, even sometimes of the village.” Today, the phenomenon seems inescapable. Google your favorite despised human group—Jews, blacks, Arabs, gays, and so on—along with words like “vermin,” “roaches,” or “animals,” and it will all come spilling out. Some of this rhetoric is seen as inappropriate for mainstream discourse. But wait long enough and you’ll hear the word “animals” used even by respectable people, referring to terrorists, or to Israelis or Palestinians, or to undocumented immigrants, or to deporters of undocumented immigrants. Such rhetoric shows up in the speech of white supremacists—but also when the rest of us talk about white supremacists.

It’s not just a matter of words. At Auschwitz, the Nazis tattooed numbers on their prisoners’ arms. Throughout history, people have believed that it was acceptable to own humans, and there were explicit debates in which scholars and politicians mulled over whether certain groups (such as blacks and Native Americans) were “natural slaves.” Even in the past century, there were human zoos, where Africans were put in enclosures for Europeans to gawk at.

Early psychological research on dehumanization looked at what made the Nazis different from the rest of us. But psychologists now talk about the ubiquity of dehumanization. Nick Haslam, at the University of Melbourne, and Steve Loughnan, at the University of Edinburgh, provide a list of examples, including some painfully mundane ones: “Outraged members of the public call sex offenders animals. Psychopaths treat victims merely as means to their vicious ends. The poor are mocked as libidinous dolts. Passersby look through homeless people as if they were transparent obstacles. Dementia sufferers are represented in the media as shuffling zombies.”

The thesis that viewing others as objects or animals enables our very worst conduct would seem to explain a great deal. Yet there’s reason to think that it’s almost the opposite of the truth.

At some European soccer games, fans make monkey noises at African players and throw bananas at them. Describing Africans as monkeys is a common racist trope, and might seem like yet another example of dehumanization. But plainly these fans don’t really think the players are monkeys; the whole point of their behavior is to disorient and humiliate. To believe that such taunts are effective is to assume that their targets would be ashamed to be thought of that way—which implies that, at some level, you think of them as people after all.

The next morning the “scrubbing parties” began. Members of the Austrian SA, working from lists, from personal knowledge, and from the knowledge of passersby, identified Jews and forced them to kneel and clean the streets with brushes. This was a ritual humiliation. Jews, often doctors and lawyers or other professionals, were suddenly on their knees performing menial labor in front of jeering crowds. Ernest P. remembered the spectacle of the “scrubbing parties” as “amusement for the Austrian population.” A journalist described “the fluffy Viennese blondes, fighting one another to get closer to the elevating spectacle of the ashen-faced Jewish surgeon on hands and knees before a half-dozen young hooligans with Swastika armlets and dog-whips.” Meanwhile, Jewish girls were sexually abused, and older Jewish men were forced to perform public physical exercise.

The Jews who were forced to scrub the streets—not to mention those subjected to far worse degradations—were not thought of as lacking human emotions. Indeed, if the Jews had been thought to be indifferent to their treatment, there would have been nothing to watch here; the crowd had gathered because it wanted to see them suffer. The logic of such brutality is the logic of metaphor: to assert a likeness between two different things holds power only in the light of that difference. The sadism of treating human beings like vermin lies precisely in the recognition that they are not.

What about violence more generally? Some evolutionary psychologists and economists explain assault, rape, and murder as rational actions, benefitting the perpetrator or the perpetrator’s genes. No doubt some violence—and a reputation for being willing and able to engage in violence—can serve a useful purpose, particularly in more brutal environments. On the other hand, much violent behavior can be seen as evidence of a loss of control. It’s Criminology 101 that many crimes are committed under the influence of drugs and alcohol, and that people who assault, rape, and murder show less impulse control in other aspects of their lives as well. In the heat of passion, the moral enormity of the violent action loses its purchase.

But “Virtuous Violence: Hurting and Killing to Create, Sustain, End, and Honor Social Relationships” (Cambridge), by the anthropologist Alan Fiske and the psychologist Tage Rai, argues that these standard accounts often have it backward. In many instances, violence is neither a cold-blooded solution to a problem nor a failure of inhibition; most of all, it doesn’t entail a blindness to moral considerations. On the contrary, morality is often a motivating force: “People are impelled to violence when they feel that to regulate certain social relationships, imposing suffering or death is necessary, natural, legitimate, desirable, condoned, admired, and ethically gratifying.” Obvious examples include suicide bombings, honor killings, and the torture of prisoners during war, but Fiske and Rai extend the list to gang fights and violence toward intimate partners. For Fiske and Rai, actions like these often reflect the desire to do the right thing, to exact just vengeance, or to teach someone a lesson. There’s a profound continuity between such acts and the punishments that—in the name of requital, deterrence, or discipline—the criminal-justice system lawfully imposes. Moral violence, whether reflected in legal sanctions, the killing of enemy soldiers in war, or punishing someone for an ethical transgression, is motivated by the recognition that its victim is a moral agent, someone fully human.

In the fiercely argued and timely study “Down Girl: The Logic of Misogyny” (Oxford), the philosopher Kate Manne makes a consonant argument about sexual violence. “The idea of rapists as monsters exonerates by caricature,” she writes, urging us to recognize “the banality of misogyny,” the disturbing possibility that “people may know full well that those they treat in brutally degrading and inhuman ways are fellow human beings, underneath a more or less thin veneer of false consciousness.”

Manne is arguing against a weighty and well-established school of thought. Catharine A. MacKinnon has posed the question: “When will women be human?” Rae Langton has explored the idea of sexual solipsism, a doubt that women’s minds exist. And countless theorists talk about “objectification,” the tendency to deny women’s autonomy and subjecthood, and to scant their experiences. Like Fiske and Rai, Manne sees a larger truth in the opposite tendency. In misogyny, she argues, “often, it’s not a sense of women’s humanity that is lacking. Her humanity is precisely the problem.”

Men, she proposes, have come to expect certain things from women—attention, admiration, sympathy, solace, and, of course, sex and love. Misogyny is the mind-set that polices and enforces these goals; it’s the “law enforcement branch” of the patriarchy. The most obvious example of this attitude is the punishing of “bad women,” where being bad means failing to give men what they want. But misogyny also involves rewarding women who do conform, and sympathizing with men (Manne calls this “himpathy”) who have done awful things to women.

As a case study of misogyny, Manne considers strangulation—almost always performed by men on female intimate partners—which she describes as “a demonstration of authority and domination,” a form of torture that often leaves no marks. Other forms of expressive violence are very much intended to leave marks, notably “vitriolage,” or acid attacks, directed against girls and women in Bangladesh and elsewhere. Catalysts for such attacks include refusal of marriage, sex, and romance. Then, there are so-called family annihilators, almost always men, who kill their families and, typically, themselves. Often, the motivation is shame, but sometimes hatred is a factor as well; and sometimes the mother of murdered children is left alive, perhaps notified by phone or a letter afterward—See what you’ve made me do. The victim is also the audience; her imagined response figures large in the perpetrator’s imagination.

Manne delves into the case of Elliot Rodger, who, in 2014, went on a killing spree, targeting people at random, after he was denied entry to a sorority house at the University of California, Santa Barbara. He slew six people and injured fourteen more before killing himself. In a videotape, Rodger, who was twenty-two, explained that women “gave their affection and sex and love to other men but never to me.” And then, talking to these women, he said, “I will punish you all for it . . . . I’ll take great pleasure in slaughtering all of you.”

Manne makes clear that Rodger wasn’t objectifying women; he was simply enraged that their capacity for love and romance didn’t extend to him. Manne’s analysis can be seen as an exploration of an observation made by Margaret Atwood—that men are afraid that women will laugh at them, and women are afraid that men will kill them. For Manne, such violent episodes are merely an extreme manifestation of everyday misogyny, and she extends her analysis to catcalling, attitudes toward abortion, and the predations of Donald Trump.

Nor are the mechanisms she identifies confined to misogyny. The aggressions licensed by moral entitlement, the veneer of bad faith: those things are evident in a wide range of phenomena, from slaveholders’ religion-tinctured justifications to the Nazi bureaucrats’ squeamishness about naming the activity they were organizing, neither of which would have been necessary if the oppressors were really convinced that their victims were beasts.

If the worst acts of cruelty aren’t propelled by dehumanization, not all dehumanization is accompanied by cruelty. Manne points out that there’s nothing wrong with a surgeon viewing her patients as mere bodies when they’re on the operating table; in fact, it’s important for doctors not to have certain natural reactions—anger, moral disgust, sexual desire—when examining patients. The philosopher Martha C. Nussbaum has given the example of using your sleeping partner’s stomach as a pillow when lying in bed, and goes on to explore the more fraught case of objectification during sexual intercourse, suggesting that there’s nothing inherently wrong about this so long as it is consensual and restricted to the bedroom.

As a philosopher, Manne grounds her arguments in more technical literature, and at one point she emphasizes the connection between her position and the Oxford philosopher P. F. Strawson’s theory of “reactive attitudes.” Strawson argued that, when we’re dealing with another person as a person, we can’t help experiencing such attitudes as admiration and gratitude, resentment and blame. You generally don’t feel this way toward rocks or rodents. Acknowledging the humanity of another, then, has its risks, and these are neatly summarized by Manne, who notes that seeing someone as a person makes it possible for that person to be a true friend or beloved spouse, but it also makes it possible for people to be “an intelligible rival, enemy, usurper, insubordinate, betrayer, etc.” She goes on:

Moreover, in being capable of rationality, agency, autonomy, and judgment, they are also someone who could coerce, manipulate, humiliate, or shame you. In being capable of abstract relational thought and congruent moral emotions, they are capable of thinking ill of you and regarding you contemptuously. In being capable of forming complex desires and intentions, they are capable of harboring malice and plotting against you. In being capable of valuing, they may value what you abhor and abhor what you value. They may hence be a threat to all that you cherish.

If there’s something missing from these approaches to violence, it’s attention to first-person attitudes, how we think about ourselves as moral agents. I can resent someone, but I can also feel shame at how I treated him or her. Fiske and Rai sometimes write as if the paradigm of moralistic violence were the final scene of the movie in which our hero blows away the terrorist or the serial killer or the rapist—a deeply satisfying act that has everyone cheering. But what about doubt and ambivalence? Some fathers who severely beat their misbehaving children, or some soldiers who engage in “punitive rape,” are confident in the moral rightness of their acts. But some aren’t. Real moral progress may involve studying the forms of doubt and ambivalence that sometimes attend acts of brutality.

In a masterly and grim book, “One Long Night: A Global History of Concentration Camps” (Little, Brown), Andrea Pitzer articulates some of the perplexities of her subject. A concentration camp exists, she says, whenever a government holds groups of civilians outside the normal legal process, and nearly all nations have had them. They can be the most savage places on earth, but this isn’t an essential feature. During the Second World War, American camps for the Japanese weren’t nearly as terrible as camps in Germany and the Soviet Union. There are even some camps that began with noble intentions, such as refugee camps set up to provide food and shelter—though they tend to worsen over time, evolving into what Pitzer describes as “permanent purgatory.”

When concentration camps are established, they are usually said to exist to protect the larger population from some suspect group, or to be part of a civilizing message, or to be a way to restrain some group of civilians from supporting hostile forces. From this perspective, concentration camps are a means to an end, an example of instrumental violence. Typically, though, the camps do have a punitive aspect. Pitzer tells of how, after the First World War, Bavaria’s Social Democratic premier, Kurt Eisner, was slow to demand that Germans be released from French and British camps; he wished instead to appeal to the Allies’ sense of humanity. Eisner was Jewish, and Hitler fumed about this “betrayal” in a speech in 1922, saying that the Jews should learn “how it feels to live in concentration camps!”

Certainly, Pitzer’s description of various concentration camps contains so many examples of cruelty and degradation that it’s impossible to see them as a mere failure to acknowledge the humanity of their victims. As the scholar of warfare Johannes Lang has observed of the Nazi death camps, “What might look like the dehumanization of the other is instead a way to exert power over another human.”

The limitations of the dehumanization thesis are hardly good news. There has always been something optimistic about the idea that our worst acts of inhumanity are based on confusion. It suggests that we could make the world better simply by having a clearer grasp of reality—by deactivating those brain implants, or their ideological equivalent. The truth may be harder to accept: that our best and our worst tendencies arise precisely from seeing others as human. ♦

This article appears in the print edition of the November 27, 2017, issue, with the headline “Beastly.”

Two new histories show how the unimaginable was systematized.

Steven Pinker’s history of violence.

As the years passed, Tom grew more entrenched in his homelessness. He was absorbed in lofty fantasies and private missions, aware of the basest necessities and the most transcendent abstractions, and almost nothing in between.